1. Field of the Invention
The present invention relates to a power source unit and a card-like memory medium, and more particularly, is suitably applied to integrated circuit (IC) cards which are to be used, for example, in a security system.
2. Description of the Related Art
There are security systems in which IC cards are given to users and each person is identified with his IC card. Such security systems uses a reader/writer which exchanges data with an IC card, to identify users by reading/writing the data from/into their IC cards.
As the security systems, there have been proposed and adopted a contact type system which exchanges data between an IC card and a reader/writer by electrically connecting to each other and a non-contact type system which exchanges data between an IC card and a reader/writer via electromagnetic waves.
In the non-contact type security system, a reader/writer first modulates data to be transmitted by a predetermined method and radiates electromagnetic waves (magnetic field) corresponding to the obtained transmission data to an IC card. The IC card receives the electromagnetic waves radiated from the reader/writer and demodulates it by a predetermined method, thereby restoring original data. The IC card generates a response signal by performing predetermined data processing on the restored original data.
The IC card modulates this response signal by a predetermined method and transmits electromagnetic waves corresponding to the obtained transmission data to the reader/writer. The reader/writer receives the electromagnetic waves transmitted from the IC card, restores an original response signal by demodulating the electromagnetic waves and operates in accordance with the response signal. By the way, an IC card which is now used is configured to operate internal circuits by utilizing a magnetic field energy of the received electromagnetic waves without using a battery.
In the contact type security system, on the other hand, the reader/writer is configured to first trigger the IC card via a connection point between the reader/writer and the IC card so that data is transmitted and received between them by the trigger.
Under the present circumstance which is a transition period where the security system is shifting to the non-contact type from the contact type, there is an increasing demand for a system which has functions of both the non-contact type and the contact type, whereby a composite IC card which has functions of both the non-contact type and the contact type has been proposed. A configuration of this composite IC card will be described below with reference to FIG. 1.
In the following description, a mode where a composite IC card 1 operates as a non-contact type and another mode where it operates as a contact type will be referred to as a remote mode and a contact mode, respectively. In the remote mode, the composite IC card 1 receives electromagnetic waves transmitted from a reader/writer (not shown) with an antenna coil 2, and sends out the energy of the electromagnetic waves to a power unit 3, a remote side data input/output unit 4, a voltage detector 5 and a carrier extraction circuit 6 via an antenna coil connection terminal CP or CM. In the contact mode, on the other hand, the composite IC card 1 supplies to the power unit 3 a source voltage which is sent from the reader/writer (not shown) via a contact side power terminal VDD or a contact side ground terminal VSS.
In the remote mode, the power unit 3 converts the electromagnetic waves energy supplied via the antenna connection terminals CP or CM into a direct voltage with a rectifier 10 and sends out the direct voltage as a service voltage Vsup to a regulator 11 and the voltage detector 5 by way of a first reverse-flow preventing diode element D1. In the contact mode, on the other hand, the power unit 3 supplies a source voltage which is sent via the contact side power terminal VDD as the service voltage Vsup to the regulator 11 and the voltage detector 5 via a second reverse-flow preventing diode element D2.
The regulator 11 is configured to keep the level of the service voltage Vsup constant and send it out to the voltage detector 5 and a logic circuit 12, thereby supplying a stable power to the voltage detector 5 and the logic circuit 12. The voltage detector 5 is configured to generate various kinds of flags for operating the logic circuit 12.
Concretely, the voltage detector 5 converts the level of the supplied service voltage Vsup into a voltage level corresponding to an internal source voltage VCC, and in the case where a converted source voltage VCC has a voltage level lower than that which is required to operate the logic circuit 12, the voltage detector 5 sends out a reset signal VRST having a logical levelxe2x80x9cHxe2x80x9d to the logic circuit 12, thereby stopping the logic circuit 12. In the case where the source voltage VCC has a voltage level higher than that which is required to operate the logic circuit 12, on the other hand, the voltage detector 5 sends out a source voltage monitor flag signal VF1 having the logical levelxe2x80x9cHxe2x80x9d to the logic circuit 12, thereby operating the logic circuit 12. Further, when the service voltage Vsup has a voltage level higher than a predetermined threshold level, the voltage detector 5 sends out an input voltage detection flag VZ having the logical level xe2x80x9cHxe2x80x9d to the logic circuit 12.
When the voltage detector 5 detects the source voltage which is supplied via the antenna connection terminal CM, it generates a remote side source voltage flag VR having the logical level xe2x80x9cHxe2x80x9d and sends it out to the logic circuit 12 and an operation mode determination circuit 15, and further when the voltage detector 5 detects the source voltage which is supplied via the contact side power terminal VDD, it generates a contact side source voltage flag VC having the logical level xe2x80x9cHxe2x80x9d and sends it out to the logic circuit 12 and the operation mode determination circuit 15.
The remote side data input/output unit 4 generates remote side input data RRx by demodulating the electromagnetic waves received by an antenna coil and sends out the data to the logic circuit 12. The logic circuit 12 generates remote side output data RTx by performing predetermined data processing on the remote side input data RRx, modulates the remote side output data RTx with the remote side data input/output unit 4 and radiates electromagnetic waves corresponding to the remote side output data RTx from the antenna coil 2.
On the basis of the electromagnetic waves received by the antenna coil 2, the carrier extraction circuit 6 extracts a remote side clock signal RCLK having the same frequency as carrier waves, and sends out the clock signal RCLK to the operation mode determination circuit 15 and a clock generator 16. In the contact mode, the composite IC card 1 inputs into a level shift circuit 17 a clock signal which is input from the contact side clock input terminal CLK. The level shift circuit 17 converts a signal level of the input clock signal into a signal level corresponding to the internal source voltage VCC, and sends out the obtained contact side clock signal CCLK to the operation mode determination circuit 15 and the clock generator 16.
On the basis of the remote side source voltage flag VR and the contact side source voltage flag VC, which are supplied from the voltage detector 5, and the remote side clock signal RCLK and the contact side clock signal CCLK, the operation mode determination circuit 15 determines an operation mode for the composite IC card 1. When a determined operation mode is the remote mode, the operation mode determination circuit 15 generates an operation mode signal Mode having the logical level xe2x80x9cHxe2x80x9d and sends it out to the clock generator 16 or when the determined operation mode is the contact mode, the operation mode determination circuit 15 generates an operation mode signal Mode having a logical level xe2x80x9cLxe2x80x9d and sends it out to the clock generator 16.
On the basis of the supplied operation mode signal Mode, the clock generator 16 selects either of the remote side clock signal RCLK and the contact side clock signal CCLK and sends the selected clock signal as a master clock signal MCLK to the logic circuit 12.
In the contact mode, the composite IC card 1 inputs data which is sent from the reader/writer via a contact side data input/output terminal I/O into a contact side data input/output unit 20. The contact side data input/output unit 20 performs a predetermined processing on the supplied data and sends out the obtained contact side input data CRx to the logic circuit 12. The logic circuit 12 generates contact side output data CTx as a response signal from the contact side input data CRx and sends it out to the contact side data input/output unit 20.
The contact side data input/output unit 20 performs predetermined data processing the contact side output data CTx and outputs it to the reader/writer via the contact side data input/output terminal I/O. Furthermore, the composite IC card 1 inputs a reset signal sent from the reader/writer into a level shift circuit 21 via a contact side reset terminal RST. The level shift circuit 21 generates a contact side reset signal CRST by converting a signal level of the reset signal into a signal level corresponding to the internal source voltage VCC and supplies the reset signal CRST to the logic circuit 12.
In the power unit 3, the input side of the diode element D1 is connected to the output side of the rectifier 10, the input side of the diode element D2 is connected to the contact side power terminal VDD, and the output sides of these diode elements D1 and D2 are connected to each other so that the service voltage Vsup is supplied to the following circuits, as described above. When such a power unit 3 is constructed, it is inevitably necessary to integrate circuits using the process of a complementary metal oxide semiconductor (CMOS) which can realize a high integration and a low cost, in order to eliminate of useless hardware. Although integrating circuits using the process of the CMOS realize the miniaturize and low cost as described above, it causes a leak current in such a power unit 3 and as a result, the electric power consumption is increased.
Now, a principle of a leak current which is caused by the CMOS process will be described. FIG. 2 shows a case where a reverse-flow preventing diode element D1 is composed of a so-called floating type diode element D1A. A diode element D2 has the same composition as the diode element D1 and will not be omitted. The floating type diode element D1A is a diode element having a structure wherein an N well is joined onto a P-type substrate adopted as ground, and an N+ layer and a P+ layer having high concentrations are joined onto the N well so that the N+ layer and the P+ layer have potentials floating from the ground.
As shown in FIG. 3, though the floating type diode element D1A is configured to supply a current in a direction indicated by an arrow xe2x80x9caxe2x80x9d by utilizing a PN junction composed of the P+ layer and the N well, it actually functions as a substrate transistor (PNP-type transistor) due to production of a parasitic transistor, thereby supplying a leak current in a direction indicated by an arrow xe2x80x9cbxe2x80x9d.
As shown in FIG. 4, in the power unit 3 where the floating type diode element D1A is used as the reverse-flow preventing diode D1, a large amount of leak current is supplied in a direction indicated by an arrow xe2x80x9ccxe2x80x9d, thereby causing problems that a communication distance between the reader/writer and the composite IC card is shortened in the remote mode and that the battery life of the reader/writer is shortened in the contact mode.
It is conceivable to use a MOS transistor TR1 which has a diode characteristic (that is, a square characteristic) in place of the floating type diode element D1A as the reverse-flow preventing circuit as shown in FIG. 5. FIG. 6 shows a structure of the MOS transistor TR1 which has the diode characteristic. The MOS transistor TR1 is composed by joining an N well onto a P-type substrate adopted as ground, joining an N+ layer as a back gate electrode BG, a P+ layer as a source electrode S, and a P+ layer as a drain electrode D onto the N well, connecting the back gate electrode BG to the source electrode S, and connecting a gate electrode G and the drain electrode D.
This MOS transistor TR1 obtains the diode characteristic and a current flows in a direction indicated by an arrow h shown in FIG. 6 when a potential Vs of the back gate electrode BG is higher than a potential Vd of the drain electrode D. However, when the potential Vs of the back gate electrode BG is lower than the potential Vd of the drain electrode D, a parasitic diode is produced and a leak current flows in a direction indicated by an arrow xe2x80x9cIxe2x80x9d shown in FIG. 6.
Therefore, as shown in FIG. 7, the power unit 3 which uses MOS transistors TR1A and TR1B as the reverse-flow preventing circuit generates a direct voltage on an output side of the rectifier 10 and applies to the drain electrode D of the MOS transistor TR1B a voltage which is higher than that to the back gate electrode BG in the remote mode, thereby generating a parasitic diode. Accordingly, the MOS transistor TR1B allows a leak current to be supplied along a path from the P+ layer through the N well to the contact side power terminal VDD, whereby the reverse-flow preventing circuit cannot function as such.
The composite IC card 1 described above adopts a clock signal generation method which generates the master clock signal MCLK by selecting either the remote side clock signal RCLK in the remote mode or the contact side clock signal CCLK in the contact mode on the basis of the operation mode Mode determined by the operation mode determination circuit 15.
When the clock generator 16 is switched to select the remote side clock signal RCLK in the contact mode, for example, the composite IC card 1 which uses the clock signal generation method cannot operate the logic circuit 12 since the contact side clock signal CCLK is not supplied to the logic circuit 12. In this case, the composite IC card 1 cannot determine the operation mode by software operation processing which uses the logic circuit 12, so that it requires hardware such as the operation determination circuit 15 and the clock generator 16, thereby causing a problem in that a circuit scale may be enlarged.
In view of the foregoing, an object of this invention is to provide a power source unit and a card-like memory medium which can be configured compact while suppressing increase in electric power consumption.
The foregoing object and other objects of the invention have been achieved by the provision of a power source unit which supplies to following electronic circuits a source voltage comprised of a direct current generated on the basis of an alternating current supplied from outside via a first input terminal or a source voltage comprised of a direct current supplied from outside via a second input terminal, depending on a condition of use. The power source unit comprises a rectifier means for converting the alternating current supplied via the first input terminal into a direct current and a reverse-flow preventing means for preventing the direct current output from the rectifier means from being supplied reversely to the second input terminal, thereby preventing the direct current supplied via the second input terminal from being supplied reversely to the first input terminal on the basis of a characteristic of the rectifier means.
The characteristic of the rectifier means is utilized to prevent the direct current supplied via the second input terminal from being supplied reversely to the first input terminals and therefore, it is not necessary to conventionally dispose a separate means which prevents the direct current supplied via the second input terminals from being supplied reversely to the first input terminals, thereby making it possible to simplify a configuration of the power source unit and reduce useless current consumption.
Then nature, principle and utility of the invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings in which like parts are designated by like reference numerals or characters.